The starter battery of a motor vehicle is, for example, a rechargeable battery which supplies the electric current for the starter of an internal combustion engine. The battery of an electric vehicle which serves to drive the vehicle is, by contrast, called the traction battery. In addition, electric vehicles or hybrid vehicles can also have a starter battery. The batteries used can be, for example, rechargeable lead-acid batteries or rechargeable lithium-ion batteries which, however, are also called lead-acid batteries or lithium-ion batteries in the text which follows.
When lead-acid batteries or rechargeable lead-acid batteries age and, for example, begin to “emit gas” on account of internal short-circuits or other mechanisms, the temperature of said batteries usually increases. In the event of greatly elevated temperatures, this can lead to the electrolyte beginning to boil and escaping from the battery. In addition, if lithium-ion batteries or rechargeable lithium-ion batteries are damaged, they can likewise become extremely hot on account of internal reactions or current flows. To this end, the state of the battery should be monitored, this being possible on the basis of various parameters.
In order to determine battery state, it is possible, for example, to monitor the battery temperature since this is an indicator of the state of the battery. This is typically performed using a conventional pole-niche sensor which serves as a battery monitoring sensor (BMS). If, for example, the temperature which is measured using this sensor reaches a specific limit value, a critical state of the battery is assumed.
However, the battery temperature can also be used in other ways when determining the level of wear of a battery. For example, EP 1 387 177 A2 discloses a method for determining the level of wear of an electrochemical energy store, in which method a wear variable with respect to time is determined depending on the battery temperature. In this case, the wear variable is determined as the sum with respect to time of temperature-dependent amounts of wear, wherein there is an over proportionate increase in the values of the amounts of wear as the temperature rises. Therefore, the over proportionate influence of increasing battery temperatures on the level of wear of the battery should be taken into account.
Vehicle systems in the deep low-voltage range (14 to 48 V) are usually separated from electrical drive systems, as can be found in electric vehicles and hybrid vehicles. However, battery monitoring is not common in low-voltage systems of this kind. However, battery monitoring has gained new importance on account of a change in user behavior, in particular in respect of unintentional charging of batteries of vehicles overnight in a garage.
When monitoring the battery temperature, for example, by means of a pole-niche sensor however, it should be noted that an increase in the temperature measured there can be affected by various influences. On the one hand, said increase may be attributed to internal heating of the battery, this indicating a weakened or damaged battery. However, it may also be partly or entirely caused by external heat sources. If temperature increases due to external heat sources are not taken into account, a monitoring system of the vehicle would frequently indicate a damaged battery or possibly even disconnect the battery from the voltage source during the course of a risk minimization strategy even though the battery is intact. This should be avoided since it has an adverse effect on the functionality of the vehicle and false alarms lead to customer dissatisfaction.